Epstein-Barr virus (EBV) is best known for its ability to infect and cause disease by immortalizing B lymphocytes. However, the virus also accesses epithelial cells with devastating consequences. It is strongly implicated in the development of nasopharyngeal carcinoma and may play a role in the emergence of certain gastric cancers. The long term goal of this research is to understand the molecular basis for the tissue tropism of EBV. Most is known about how EBV enters B cells. A current model proposes that virus uses minimally an attachment protein gp350/220 which binds to the complement receptor type 2 (CR2) and a complex of three glycoproteins gH-gL-gp42 which is involved in penetration. Successful penetration requires that gp42 bind to HLA class II which functions as a coreceptor on the B cell surface. Entry into epithelial cells is very different. A current model for epithelial cells proposes that entry requires neither use of CR2 nor an interaction between gp42 and HLA class II. Instead, new findings suggest the existence of both a novel receptor and a novel coreceptor on epithelial cells. The immediate goal of this application is to test these models with four specific aims. The first aim is to identify the coreceptor that enables a virus that lacks gp42 to infect epithelial cells. The second aim is to explore and compare the interactions of the gH complex with B cells and epithelial cells. The third aim is to identify the viral glycoprotein used by EBV to attach to CR2- negative epithelial cells. The final aim is to identify the receptor used by EBV to infect CR2-negative epithelial cells. Identification of receptor and coreceptor will be addressed by transfecting appropriate cells with epithelial cell cDNA expression libraries. Transfected cells will be probed with recombinant viruses lacking gp42, or expressing green fluoroscent protein. Interactions of cells with the gH complex will be explored by mutational analysis and complementation of virus lacking gH. Recombinant proteins, antibodies and viruses lacking a variety of glycoproteins will be used to identify the epithelial cell attachment protein. Dissection of the molecular events that enable EBV to access the cells it infects is critical to understanding the biology of this important human pathogen.